1 简介
多进制正交幅度调制,结合了幅度和相位两个要素,信号均匀分布,频谱利用率高.文中介绍了正交幅度调制解调原理,通过系统仿真实验,对16QAM的调制解调过程,原理进行了论证分析,给出了高斯白噪声干扰下的误码率.仿真实验结果说明了,多进制正交幅度调制解调功率,带宽高效,易于实现,误码率低,抗干扰能力强.
2 部分代码
clc;clear;%% 长度N（1 -1）比特序列产生N = 4e4; %设置比特序列的长度t = 1:1:N;data = randi(2,1,N)-1;% data = [1 1 0 1 0 0 1 1 1 1 0 1 0 0 1 1 0 1 1 1];figure(1)plot(data(1:40),'*')axis([0 41 -0.2 1.2])title('图1 原始数据序列');xlabel('t');ylabel('数据值');grid on;%% 16QAM调制data_modu = QAM16_modu( data );figure(2)subplot(2,1,1)plot(real(data_modu(1:10)),'*');title('图2-1 16QAM调制数据的实部');xlabel('t');ylabel('数据值');axis([0 11 -4 4]);grid on;subplot(2,1,2)plot(imag(data_modu(1:10)),'*')title('图2-2 16QAM调制数据的虚部');xlabel('t');ylabel('数据值');axis([0 11 -4 4]);grid on;%% 8倍插值data_upsam = upsample(data_modu,8);figure(3)subplot(2,1,1);plot(real(data_upsam(1:80)),'*');title('图3-1 16QAM调制数据8倍插值后的实部');xlabel('t');ylabel('数据值');axis([0 81 -4 4]);grid on;subplot(2,1,2);plot(imag(data_upsam(1:80)),'*')title('图3-2 16QAM调制数据8倍插值后的虚部');xlabel('t');ylabel('数据值');axis([0 81 -4 4]);grid on;%% 设置均方根升余弦滤波器的参数beta = 0.25;span = 6;sps = 4;b = rcosdesign(beta, span, sps, 'sqrt');%% 发射端均方根成型滤波——低通滤波data_low1 = conv(data_upsam, b);figure(4)subplot(2,1,1)% span*sps/2+1 data_low1(1:80)plot(real(data_low1((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);title('图4-1 发射端低通滤波后的实部');xlabel('t');ylabel('数据值');% axis([span*sps/2+1 span*sps/2+80 -2 2]);grid on;subplot(2,1,2)plot(imag(data_low1((span*sps/2+1):(span*sps/2+80))),'LineWidth',1)title('图4-2 发射端低通滤波后的虚部');xlabel('t');ylabel('数据值');% axis([span*sps/2+1 span*sps/2+80 -2 2]);grid on;%% 信道加性高斯白噪声%SNR与EbN0之间的关系SNR = EbN0 + 10log10(NBits * Coderate) - 10log10(0.5or1 * upfactor)BER = zeros(1,15);NBits = 4;Coderate = 1;upfactor = 8;% for EbN0 = 1:1:15EbN0 = 10;SNR = EbN0 + 10*log10(NBits * Coderate) - 10*log10(1 * upfactor);data_awgn = awgn(data_low1,SNR,'measured');figure(5)subplot(2,1,1)plot(real(data_low1((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);hold on;plot(real(data_awgn((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);title('图5-1 加噪声前后数据的实部');xlabel('t');ylabel('数据值');legend('噪声前','噪声后');% axis([span*sps/2+1 span*sps/2+80 -4 4]);grid on;subplot(2,1,2)plot(imag(data_low1((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);hold on;plot(imag(data_awgn((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);title('图5-2 加噪声前后数据的虚部');xlabel('t');ylabel('数据值');legend('噪声前','噪声后');% axis([span*sps/2+1 span*sps/2+80 -4 4]);grid on;%% 接收端均方根滤波——低通滤波data_low2 = conv(data_awgn, b);% data_low2 = conv(data_low1, b);data_window = data_low2( (span*sps+1):(span*sps+length(data_upsam)) );figure(6)subplot(2,1,1)plot(real(data_low1((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);hold on;plot(real(data_awgn((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);plot(real(data_window(1:80)),'LineWidth',1);title('图6-1 加噪声及滤波前后数据的实部');xlabel('t');ylabel('数据值');legend('噪声前','噪声后','滤波后');grid on;subplot(2,1,2)plot(imag(data_low1((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);hold on;plot(imag(data_awgn((span*sps/2+1):(span*sps/2+80))),'LineWidth',1);plot(imag(data_window(1:80)),'LineWidth',1);title('图6-2 加噪声及滤波前后数据的虚部');xlabel('t');ylabel('数据值');legend('噪声前','噪声后','滤波后');grid on;%% 1/8倍采样data_downsam = downsample(data_window,8,0);figure(7)subplot(4,1,1);[f2,xi2] = ksdensity(real(data_modu)); %发射信号实部的PDFplot(xi2,f2);title('发射端16QAM调制之后信号实部的pdf');axis([-5 5 0 0.3])grid on;subplot(4,1,2);[f22,xi22] = ksdensity(imag(data_modu)); %发射信号实部的PDFplot(xi22,f22);title('发射端16QAM调制之后信号虚部的pdf');axis([-5 5 0 0.3])grid on;subplot(4,1,3)[f7,xi7] = ksdensity(real(data_downsam)); %接收信号实部的PDFplot(xi7,f7);title('接收端下采样之后信号实部的pdf');axis([-5 5 0 0.3])grid on;subplot(4,1,4)[f72,xi72] = ksdensity(imag(data_downsam)); %接收信号虚部的PDFplot(xi72,f72);title('接收端下采样之后信号虚部的pdf');axis([-5 5 0 0.3])grid on;%% 16QAM星座点判决data_Judge = QAM16_Euclid_Judge( data_downsam );%% 16QAM解调data_demodu = QAM16_demodu( data_Judge );figure(8)subplot(2,1,1)plot(data(1:40),'*');axis([0 41 -0.2 1.2])title('图8-1 原始数据序列');xlabel('t');ylabel('数据值');grid on;subplot(2,1,2)plot(data_demodu(1:40),'*');axis([0 41 -0.2 1.2])title('图8-2 接收数据序列');xlabel('t');ylabel('数据值');grid on;% %% 解调数据与原始数据比较并计算误码率% n = length(find(data_demodu-data));% BER(EbN0) = n/N% end% %% 求得理论误比特率% EbN0 = 1:1:15% BER0 = berawgn(EbN0,'qam',16);% % %% 理论误比特率与仿真误比特率的比较% figure(9)% semilogy(EbN0,BER,'-o','LineWidth',1);% hold on;% semilogy(EbN0,BER0,'-o','LineWidth',1);% xlabel('EbN0 / dB');% ylabel('BER');% title('图9 理论误比特率与仿真误比特率的比较')% legend('实际BER','理论BER');% grid on;
3 仿真结果
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4 参考文献
[1]丁业兵, 王子武, 谭学琴. 16QAM通信系统的MATLAB实现[J]. 微型电脑应用, 2017, 33(2):3.
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